1. Field of the Invention
This invention relates generally to processing of computer graphics for display on a television, and more particularly, to the simultaneous flicker filtering and vertical contraction of computer graphics.
2. Description of the Related Art
As the result of the continuous development of new technologies, the distinction between computers, in particular computer monitors, and televisions is becoming increasingly blurred. In other words, the computer and television industries are converging. For example, computer networks such as the Internet and the World Wide Web used to be almost exclusively a computer phenomena. Now, however, televisions may also be used to access these networks. As another example, broadcast entertainment used to belong squarely in the television domain. Now, however, many service providers are offering entertainment to computer users through computer networks. As a result of this convergence, there is a need to display computer graphics intended for computers on televisions.
Televisions and computers, however, generally use incompatible graphics formats. For example, a non-interlaced 640 .times.480 data format is common among computer monitors and LED displays, especially desktop and laptop versions. In this format, each frame of computer graphics is represented as 480 horizontal lines consisting of 640 pixels each, and the entire frame is updated at once. In contrast, consider the NTSC format, a common television format. This format consists of 484 active horizontal lines, only approximately 420 of which are displayed, the actual number displayed varying from one television set to another. In addition, the NTSC format is interlaced, meaning that the frame is divided into odd and even fields and only one field or half the frame is updated at a time.
As a result, in order to display computer graphics on a television, the computer graphics often improve image quality by flicker filtering. Flicker filtering reduces visual effects that arise as a result of the conversion from a non-interlaced to an interlaced format. Vertical contraction squeezes the larger computer format into a smaller television format. Using the two example formats described above, the 480 lines of computer graphics would be vertically contracted to fit into the 420 lines of television display.
The prior art has attempted to accomplish flicker filtering using a variety of techniques known in the art, such as using low pass filters. However, one problem with existing techniques is that they require several line buffers which in turn increases the complexity and cost of converting computer graphics to a useful television format.
Thus, there is a need to simultaneously perform flicker filtering and vertical contraction. In addition, there is a need to perform these operations while minimizing hardware requirements.